1. Field of Invention
The invention relates to electrolytic apparatus and to electro-deposition of a metallic substance onto a substrate.
2. Description of Prior Art
Electro-deposition is a method which has long been used for forming adherent plating or thin non-adherent plating which can subsequently be separated from the substrate as an extra-thin foil.
As is known, in this method the speed of deposition of the metal depends inter alia on the current density used, and the practical obtainment of the current density is in return related to the "turbulence" of the electrolyte.
As is also known, the cost of an electrolysis operation depends inter alia on the potential difference between the electrodes, which can be lowered by decreasing the distance between the electrodes.
If the electrolysis operation is to be economic, therefore, the electrolyte must be conveyed at high speeds between two electrodes which are as close as possible.
The problem has already received various solutions, mainly consisting in sending the electrode at a tangent or perpendicular to the surfaces of the electrodes present. These solutions, however, are applicable only to small electrodes. When the surfaces are large, as e.g. when coating a wide steel plate or strip or during manufacture of wide thin foils by electroforming, the pressure drops are enormous owing to the small flow section and the large distance travelled by the electrolyte. In such cases, very powerful pumps have to apply very high pressures to drive the electrolyte. These pressures in turn exert considerable forces on the electrodes and may deform them, resulting in uncontrollable variation in their spacing and destroying the uniformity of electrolysis.